1. Field of the Invention
The present invention relates to a method for manufacturing carbon/silicon-carbide composite used as a thermal resistant and an anti-oxidation component, in more detail, relates to the heat processing and infiltration process needed for the manufacturing method.
2. Description of the Background Art
A rocket engine using a solid and liquid fuel needs the material that has high physical properties chemically and mechanically. This material has many advantages that improves the function of the rocket engine and reduces the weight. And in order to improve the anti-oxidation function of carbon/carbon composite commonly used as a material of thermal structure, an anti-oxidation layer is formed on the surface of the material or a reinforcement and a matrix are replaced with the material strengthened in the anti-oxidation function. This carbon/carbon composite improved as described above is called ‘Advanced Carbon Carbon’ or ‘Reinforced Carbon Carbon’, and it is applied to the design and fabrication of the components in the thermal-resistant structure. This material is usually used in components of the ultrasonic aeroplane and liquid propulsion section, after 1990s, new material and process is developed and used as an important component of the solid propulsion section. In the burning environment of the solid propulsion section of high temperature (3000K) and high pressure (1500 psi), the method that increases the anti-oxidation of the inside of the material is used as the anti-oxidation coating method of the thermal resistant components because rapid abruption near the barrier of anti-oxidation layer and the matrix layer (especially, near the nozzle throat) make the heterogeneous ablation generate. Specifically, the object of the material development is decided in the way of adding high value and of protecting the ecosystem, the development of composite containing ceramic, which can lower the pollution, is increased. Carbide, Boride, Nitride, Oxide, Silicede, and about 80 other compounds are known as carbon fiber reinforced fire resistant chemical compound. In the development of these materials, the physical and chemical affinity of the respective factors, interaction between the phases, and the effect by chemical and diffusion reaction are to be considered. Because the three effects described above apply as an important factor in the operation process of high temperature and in the real application circumstances. The physical characteristic of the compound is decided by the two former factors, the latter decides the processing condition and the maximum temperature that the material can endure. In hot temperature, the carbon and the refractory material form a eutectoid, although the sublimation point of the carbon is about 3000° C., when it becomes a compound like Carbide, Boride, Nitride, Oxide, the melting point is lowered gradually to about 1000° C. Carbide compound is used as ultra-high temperature compound material because it has a high melting point and can maintain its mechanical properties for a long period in the high temperature among those compounds.
The chemical ablation of the carbon/carbon composite begins with the oxide reaction of air pore inside the material and of activated carbon, accompanying with diminishing of the mechanical properties of the material because of burning the carbon fiber itself. Principal reason for ablation of the carbon/carbon composite is the oxide reaction made in the air pore inside the material in air environment (pressure 0.01˜1 atm), therefore raising of the oxide-resistance was considered significantly in the process of developing the carbon-based composite. Usually, two methods for increasing the oxide-resistance were considered. First method is to restrain the oxide reaction by forming a SiC layer on the carbon/carbon composite. However, as the temperature is increased, the oxide reaction between the carbon and the oxygen reaches to the boundary of the coated layer, then the layer is ablated rapidly. The ablation of the coated layer is also caused by the difference of the thermal expansion coefficient between the matrix layer and the coated layer. And, the components of the ultrasonic aeroplane are mechanically aged by impacting with granules of gravel, sand, and hail, etc. The second method is to add carbide compound, that is, a refractory compound to the material in order to increase the mechanical strength, stiffness, thermal shock resistance, and oxide-resistance of the carbon fiber compound material. A gas phase infiltration method and liquid phase infiltration method are used and usually, gas phase infiltration method is commercially used and components using that method are produced. However, initial investment costs too much and fabricating period takes more than 5 months.
On the other hand, a sintered product using metal silicon is disposed in the U.S. Pat. No. 4,238,433, but that method has difficulty in using complex preform and it is used usually as powder preform and 2 dimensional geometric form. Also, a high-density silicon carbide/carbon-graphite composite and fabrication method of the same is disposed in the U.S. Pat. No. 5,422,322, the method is to compound the carbon and inorganic matter formed in powder shape with a solvent. This method increases the SiC content inside while increases the carbon content on the surface, and is used to mechanical seal component needed lubricating ability and to bearing. However, in making a large structure, the compounding process is very complex and it is hard to observe the compound consumption at a certain rate. In addition, because of the low thermal shock resistance that the powder preform has, it can not be used in high heat load.
A 3 dimensional preform based on the carbon/phenolic preform having economical advantages has not been used because it is hard to adjust carbonization condition and high temperature heat processing condition and in the infiltration process of the metal silicon, the carbonized product is damaged, thereby thermal and structural properties become worse. Therefore, it is not applied to produce components for thermal structure.